Method and apparatus of suspension polymerization

ABSTRACT

A method of suspension polymerization of a monomeric composition to produce a polymer or a polymer composition is disclosed which method comprises the steps of retaining a disperse phase component composed of the monomeric composition and a continuous phase component composed of a medium in independent vessels, supplying the disperse phase component and the continuous phase component from their respective vessels into a disperser simultaneously and continuously through associated independent passageways, applying shear force in the disperser to form a dispersion having droplets of a desired size, subsequently introducing the dispersion into a polymerization vessel, and completing a polymerizating reaction to produce a polymer or a polymer composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing particles ofpolymerization products, particularly those having controlled particlesizes and size distributions, that are suitable for use in the powdermaking industry. Examples of the products include gap retainers, slipimparting agents, functional carriers, monodispersed particles havingsurface activity, standard particles, toners, and functional fillersthat control the fluidity and gloss characteristics of paints. Moreparticularly, the present invention relates to an improved process forproducing particles having a size of 5-50 μm by suspensionpolymerization.

2. Background of Related Art

The importance of powder making technology which takes advantage of thevarious functions of particles per se is increasingly recognized thesedays. Among the particles produced by this technology are gap retainers,slip imparting agents, functional carriers, monodispersed particleshaving surface activity, standard particles, toners, and functionalfillers that control the fluidity and gloss characteristics of paints.In order to produce these particles by polymerization, emulsionpolymerization is used most commonly today. In speciality applications,other methods of polymerization are employed, such as soap-freepolymerization, dispersion polymerization, seed polymerization andswelling polymerization.

However, these methods of polymerization have several defects. Forexample, considerable difficulty is involved in removing non-negligibleimpurities such as emulsifiers. Second, the size of particles that canbe produced is limited. Third, the production cost is exorbitant.Fourth, these methods are too complex to be suitable for large-scaleproduction. Particles having a narrow size distribution are in mostcases produced by emulsion polymerization but the size of particles thatcan be produced by this method is only about 1 μm at maximum andproducing larger particles is extremely difficult.

Suspension polymerization is also capable of producing particles,however the only products obtained so far are nonuniform in particlesize and have a broad particle size distribution. Since particle sizeand size distribution are closely related to the performance of polymerproducts in such aspects as mechanical strength, chemical resistance,color, transparency and moldability, improvements in those factors aredesired. In suspension polymerization, the liquid droplets dispersedunder agitation have various sizes and during dispersion they aresubjected to repeated breadkup and coalescence to produce particleshaving an extremely broad size distribution. For this reason, it is verydifficult to produce by suspension polymerization those particles whichhave as narrow a size distribution as monodispersed particles. Underthese circumstances, one of the objectives in the powder making industryis to establish a simple technique of suspension polymerization that iscapable of producing homogeneous particles.

The mechanism by which particles are produced by suspensionpolymerization is as follows. A disperse phase and a continuous phaseare broken up by applied energy, such as agitation, to form dropletsthat are dispersed in the continuous phase. The droplets, if they areleft as they are, are generally unstable and undergo repeated breadkupand coalescence, but eventually they are supplied with energy, such asheat, to be polymerized to form rigid and stable particles that are nolonger capable of breadkup and coalescence. Therefore, in order tocontrol the size of particles produced by suspension polymerization, onemay control in some way the size of the droplets and the process oftheir breadkup and coalescence. In fact, however, there are many factorsthat relate to the size of the droplets, such as the characteristics ofa disperser (which is hereinafter referred to as a "granulator"), itsconstruction, shape, rotational speed, size, or the size and shape ofthe reaction vessel, the amount in which the reaction solution ischarged, or the ratio between disperse and continuous phases in thereaction solution, its viscosity, as well as the type and amount of adispersant used, and it is practically impossible to control all ofthese factors in a desired way. Therefore, in practice, some of thesefactors have to be fixed so that suitable conditions for producingdesired particles are determined with the other factors being varied.

However, this approach depends so much upon a trial-and-error basis thatit is not readily adaptable to design changes such as scale-up of theprocess. This is a serious obstacle to the production of desiredparticles and the process lacks flexibility, particularly for thepurpose of producing particles that are to be used in powder form.

The present invention has been accomplished under these circumstancesand an object of providing a method of suspension polymerization that iscapable of producing smaller particles having a size distribution beingcontrolled in an easy way.

SUMMARY OF THE INVENTION

As a result of the intensive studies conducted in order to solve theaforementioned problems of the prior art, the present inventors found anew method of production that solves those problems in a simple way.

The present invention relates generally to a method of suspensionpolymerization comprising the step in which a disperse phase composed ofan addition polymerizable monomeric composition and a continuous phasecontaining a suspension stabilizer and other necessary dispersive aidsare respectively retained in independent vessels and are suppliedcontinuously into a granulator in controlled proportions throughassociated independent passageways to form a suspension having a groupof polymerizable droplets of a desired size, and the step of recoveringthe suspension from the granulator and supplying it into apolymerization vessel in which a polymerization reaction is completed toproduce a polymer. The method is characterized in that the disperse andcontinuous phases are supplied independently into a shear forcegenerating field within the granulator, where a suspension is formed byshear force and allowed to leave the shear force generating fieldthrough a clearance of a specified size provided in that field, wherebythe suspension having a group of polymerizable droplets of a desiredsize is produced.

In the method described above, the granulator generates shear force witha rotating part that preferably rotates at a speed of 3,000-50,000 rpm,more preferably at 10,000-30,000 rpm. The rotating part that generatesshear force in the granulator is spaced from the stationary part by agap of preferably 0.01-5.0 mm, more preferably 0.05-2.0 mm.

In order to control the size of particles produced by suspensionpolymerization, it is important to control the size of dropletsundergoing polymerization reaction. The droplets are broken up byturbulent energy due to the agitation of the reaction solution. On theother hand, the droplets coalesce upon mutual contact. The final size ofdroplets is determined by the balance between these processes ofbreadkup and coalescence. As regards breadkup, the present inventorsstudied various methods for producing droplets having a size range notgreater than 50 μm and found that the impact (shear force) created byblades in the dispersing apparatus was a predominant factor incontrolling the size of droplets. The size of droplets formed bybreadkup under the impact of blades depends on such factors as the stateof droplets before breadkup, the intensity of shear force and the numberof shear cycles. Droplets are subjected to shear force of the samestrength irrespective of their size, so large droplets are broken upinto smaller sizes under shear force but even if small droplets aresupplied into an area where shear force is applied, they are furtherbroken up into even smaller sizes until they are eventually emulsified.The emulsified components can no longer coalesce to form large particlesand they are simply wasted (loss). In ordinary dispersers, dropletscarried by circulating streams produced under agitation are broken upinto smaller sizes when they pass through the shear region; at the sametime, those droplets may also be broken up into smaller sizes byturbulent energy in a turbulent field created throughout the apparatus.However, the movement of droplets flowing within the apparatus is closeto a random movement, so the generated droplets are likely to have alarger diameter distribution. Therefore, in order to achieve optimalcontrol of particle size distribution, it is important that all dropletsof interest be exposed to shear force under as equal conditions aspossible and that a dispersion to be dispersed having a constant stateshould be supplied to the area of a dispersing apparatus where shearforce is applied.

As regards the coalescence of droplets, it is considered to occur as aresult of mutual contact of droplets. Generally, the smaller the size ofparticles, the greater the surface energy per unit volume and thestabler the particles that are available. Further, the factor thatcontributes to a broader size distribution is the presence of both largeand small particles in the same system. Small particles tend to beabsorbed by large particles with which they collide. However, in orderto make particles sufficiently small to have an adequately stableinterfacial energy, a correspondingly large energy must be supplied, soit is effective to divide the particles as they are concentrated in asmall shear region. In addition, it is essential to provide a conditionthat insures regular breadkup in such a way that shear force will beapplied uniformly to all the particles present.

The present invention has been accomplished on the basis of theseobservations. In accordance with the present invention, a disperse phaseand a continuous phase are supplied via independent passages directlyinto a shear force producing field (shear region) in a dispersingapparatus at desired flow rates in specified proportions and the twophases, as they are mixed together under applied shear force, aredispersed to form droplets. In this instance, dispersing conditions suchas the amount of droplets that pass through the shear region, their sizeand the ratio of disperse to continuous phase are placed under precisecontrol to insure that both the disperse phase and continuous phases(phase ratio) are subjected to shear force under conditions that arekept constant, whereby droplets having a narrow size distribution areobtained. If particles of the desired size cannot be obtained by asingle passage through the shear region, another dispersing apparatusmay be provided so that the dispersion that passed through the firstdispersing apparatus is passed through the second apparatus. In otherwords, the process described above may be repeated as many times asrequired.

The granulator to be used in the present invention is described belowmore specifically. For efficient production of fine particles, it isparticularly important to control the shear region of the granulator.

A field of shear force generation in granulators is generally composedof a stationary part (stator) and a rotating part (rotor). It should,however, be mentioned that the part corresponding to the stationary partmay be designed to be rotatable with a view to improving the efficiencyof dispersion. In any case, the field of shear force generation which isnecessary to disperse a dispersion may be regarded to lie in the gapbetween the stationary and rotating parts. In ordinary granulators,rotating blades as in a turbine are used as the rotating part, and thefield of shear force generation which is needed to form the perticles of50 μm or less is provided by the gap between the periphery of turbineblades and the stationary part. Hence, the area over which shear forceis generated is determined by a cross-sectional area of the turbineblades and it is difficult to increase of otherwise adjust that area.Further, the stationary part is usually provided with a liquid passagearea, or a space that aids in fluid passage. Since no effective shearforce is generated in this space, it is another factor that preventseffective granulation. Furthermore, this passage area is unable toprevent the presence of a solution to be granulated that failsstochastically to pass through the shear region in a satisfactory wayduring granulation. Therefore, the particles granulated with ordinarygranulators have such a rough grain size distribution that more grainsare present on the side of larger size. As a consequence, the roughgrain size distribution of such particles has a tendency to broaden,which is by no means desirable for the purpose of obtaining particleshaving a narrow size distribution.

The present inventors made intensive efforts to solve these problems andfound that when using a granulator in which the space for the field ofshear force generation was made comparatively small and in which saidfield had a specified clearance (for restricting the size of droplets)through which the dispersion to be granulated that consisted of adisperse phase and a continuous phase had to pass by all means, fineparticles having a narrow side distribution could be produced in a veryeffective way. The width of the clearance through which the dispersionis discharged can be adjusted to an optimal value in accordance with thedesired average particle size or the desired spread of sizedistribution, whereby particles having the desired size and distributioncan always be obtained.

The present inventors conducted further studies on the method ofsuspension polymerization of their own. As a result, they found thatwhen a tubular rotating part having a smooth outer surface was used in adisperser in combination with a stationary part that had substantiallythe same internal shape as that rotating part in order to improve theefficiency of shearing action, an effective shear field was formed,thereby enabling fine particles of a narrow size distribution to beproduced in a very effective manner.

The method of another aspect of the present invention generally relatesto suspension polymerization of a monomeric composition to produce apolymer or a polymer composition and this method comprises the steps ofretaining a disperse phase component composed of the monomericcomposition and a continuous phase component composed of a medium inindependent vessels, supplying the disperse and continuous phasecomponents from their respective vessels into a disperser simultaneouslyand continuously through associated independent passageways, applyingshear force in said disperser to form a dispersion having droplets of adesired size, subsequently introducing the resulting dispersion into apolymerization vessel, and completing a polymerization reaction toproduce a polymer or a polymer composition. The method is characterizedin that the disperser comprises a stationary part having a smooth innersurface and a tubular rotating part that is rotatably provided withinthe stationary part and that has a smooth outer surface.

The term "a tubular rotating part having a smooth outer surface" as usedherein means a tubular rotating part having a flat surface that is notprovided with any particular asperities, and the same applies to the"stationary part having a smooth inner surface".

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the method of the present invention;

FIG. 2 is a cross-sectional view showing an example of the granulatorthat can be used in the method of the present invention;

FIG. 3 is a graph showing the size distribution of the polymer particlesproduced in Example 1;

FIG. 4 is a graph showing the size distribution of the polymer particlesproduced in Comparative Example 1;

FIG. 5 is a graph showing the size distribution of the polymer particlesproduced in Example 2;

FIG. 6 is a graph showing the size distribution of the polymer particlesproduced in Comparative Example 2;

FIG. 7 is a longitudinal section of the disperser for use in the presentinvention;

FIG. 8 is a graph showing the size distribution of the polymer particlesproduced in Example 3;

FIG. 9 is a graph showing the size distribution of the polymer particlesproduced in Example 4; and

FIGS. 10 to 12 show modifications according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method of suspension polymerization of the present invention isdescribed below with reference to the accompanying drawings.

As shown in FIG. 1, the apparatus to be used in the practice of thepresent invention comprises a vessel 1 containing a continuous phase anda vessel 2 containing a disperse phase and equipped with a condenser 6,and the continuous and disperse phases are simultaneously supplied inspecified proportions into a granulator via associated metering pumps 4.In the granulator 5, the disperse phase is suspended in the continuousphase under applied shear force, so that droplets of sizes in a certainrange are produced, the suspension is discharged from the granulator 5and directed into a reaction vessel 3 equipped with a condenser 6 andsurrounded with a heating jacket 7. With the necessary heat beingsupplied from the jacket 7, a reaction polymerization is a completed toproduce small and uniformly sized particles having a narrowdistribution.

An example of the granulator 5 is shown in FIG. 2. It has two inlets 9and 10 in the bottom of a casing 8 through which the disperse phase andthe continuous phase are respectively introduced into a shear forcegenerating field 11. The shear force generating field 11 is composed ofa stationary part 12 that is positioned below a rotating part 13 with asmall gap provided therebetween. The surface of the shear forcegenerating field is provided with random asperities having a height of2-3 mm.

The rotating part 13 is rotated by means of a shaft 14 to produce asuspension by shear force within the shear force generating field 11.Both ends of the shear force generating field are provided with aclearance 15 of no more than about 1.8 mm which serves to restrict thedischarge of suspension. The dispersion (suspension) passing throughthis clearance is discharged at an outlet 16 in the upper part of thegranulator to be guided into the reaction vessel 3.

By the procedure described above, polymer particles not larger than 30μm that have been considered to be difficult to produce by the prior artcan be easily manufactured on an industrial scale. As a particularadvantage, fine particles as small as 2-3 μm can be manufactured by themethod of the present invention.

If the polymer particles become increasingly viscous as the suspensionpolymerization proceeds in the reaction vessel, the adhesive force ofthe particles will increase and even if agitation is performed,coalescence of those particles cannot be prevented; as a result, theparticles will either grow in size or gel. In order to prevent thesephenomena, suspension stabilizers and other aids are preferably used.

The materials that are used in performing suspension polymerization inaccordance with the present invention are described below.

Suspension Stabilizer

Suspension stabilizers that are commonly used in suspensionpolymerization are water-soluble polymers having both a hydrophilic anda hydrophobic group in the molecule. Suspension stabilizers are thosecompounds in which polar groups such as a hydroxyl group, a carboxylgroup or a salt thereof, and a sulfone group or a salt thereof arepresent as hydrophilic groups and nonpolar groups such as an aliphaticgroup and an aromatic group are present as hydrophilic groups and whichare capable of stabilizing the granulated particles of polymericcomposition by preventing their coalescence.

Examples of such suspension stabilizers include polyvinyl alcohol,casein, gelatin, cellulosic derivatives such as methyl cellulose,methylhydroxypropyl cellulose and ethyl cellulose, starch and itsderivatives, poly(meth)acrylic acid and salts thereof. Inorganic powderssuch as calcium phosphate powder and a fine silica powder are also oftenused as suspension stabilizers. These suspension stabilizers cover thesurfaces of droplets so that they will not coalesce or agglomerateduring polymerization. If desired, surfactants such as sodiumdodecylsulfonate and sodium dodecylbenzenesulfonate may be added as aidsfor suspension stabilizer.

Pigment and Polymerizable Monomer

The polymerizable monomers to be used in the present invention may besubjected to polymerization reaction in the presence of additives suchas pigments. For example, if pigments such as carbon black is added tothe polymerizable monomers, they can be readily used in the manufactureof electrophotographic toners.

Polymerizable monomers that can be used in the present invention includevinyl monomers such as styrene, α-methylstyrene, divinylbenzene,acrylonitrile, acrylate esters and methacrylate esters and/or mixturesthereof.

Polymerization Initiator

Polymerization initiators that can be used in the present invention arethose which are commonly used in the radical polymerization of vinylmonomers, as exemplified by organic peroxides such as benzoyl peroxideand butyl perbenzoate, and azo compounds such as azobisisobutyronitrile.These polymerization initiators may be used as dissolved in a solutionof the polymerizable monomers described above, These polymerizationinitiators are usually added in an amount of ca. 0.1-10%, preferably0.5-5%, of the weight of the polymerizable mixture.

EXAMPLES

The following examples and comparative examples are provided for thepurpose of further illustrating the present invention but are in no wayto be taken as limiting the invention.

Example 1

A solution as a continuous phase was prepared by dissolving polyvinylalcohol (product of Tokyo Kasei K.K.; degree of polymerization, ca.2,000; degree of saponification, ca. 80%) and sodium sulfate in water inrespective amounts of 1% and 3% of water. The thus prepared continuousphase was charged into the container 1 shown in FIG. 1. A disperse phasewas prepared by dissolving 15 g of 2,2'-azobisisobutyronitrile in amixture of styrene (400 g) and butyl acrylate (100 g) and charged intothe container 2 shown in FIG. 1.

In the next step, the disperse phase of the monomeric composition andthe continuous phase were supplied into the granulator 5 shown in FIG. 2at respective flow rates of 100 ml/min and 400 ml/min. The granulatorwas run at a rotational speed of 9,000 rpm, with the rotor 11 having adiameter of 50 mm. By this treatment in the granulator of the continuousand disperse phases that were supplied in the proportions specifiedabove, a dispersion was obtained at the outlet of the granulator andthat contained fine and uniformly sized droplets of the polymerizablemonomers. The dispersion was then directed into the polymerizationreactor 3 equipped with a turbine impeller. The inside of thepolymerization reactor had been filled with nitrogen gas and withagitation by means of the turbine impeller at 300 rpm, polymerizationwas performed for 8 hours. The end point of polymerization was confirmedby the usual method adopted in suspension polymerization.

The polymer composition thus obtained wad cooled, filtered, washedthoroughly with water and centrifuged to produce a slurry of polymerparticles.

The size of the polymer particles was measured with a Coulter counter(aperture, 100 μm and the results are shown by a size-frequency curve inFIG. 3. As shown, the polymer particles obtained in Example 1 had anarrow size distribution, with the frequency of occurrence being thehighest for particles having a size of ca. 5.5 μm.

Comparative Example 1

Suspension polymerization was performed as in Example 1 except that therotor in the granulator was a turbine impeller consisting of fourblades.

The size of the polymer particles obtained was measured with a Coultercounter (aperture, 100 μm) and the results are shown by a size-frequencycurve in FIG. 4. As shown, the frequency of occurrence was the highestfor particles having sizes of ca. 7.0-8.0 μm but the polymer particlesobtained in Comparative Example 1 had a broader size distribution thanthose obtained in Example 1.

Example 2

A solution as a continuous phase was prepared by dissolving calciumphosphate and sodium dodecylsulfonate in water in respective amounts of3% and 0.03% of water. The thus prepared continuous phase was chargedinto the container 1 shown in FIG. 1. A disperse phase was prepared bydissolving 15 g of 2,2'-azobisisobutyronitrile in a mixture of styrene(400 g) and butyl acrylate (15 g) and charged into the container 2 shownin FIG. 1. The subsequent procedures were the same as in Example 1.

The size of the polymer particles obtained was measured with a Coultercounter (aperture, 100 μm) and the results are shown by a size-frequencycurve in FIG. 5. As shown, the polymer particles obtained in Example 2had a narrow size distribution, with the frequency of occurrence beingthe highest for particles having a size of ca. 5.5 μm.

Comparative Example 2

Suspension polymerization was performed as in Example 2 except that therotor in the granulator was a turbine impeller consisting of fourblades.

The size of the polymer particles obtained was measured with a Coultercounter (aperture, 100 μm) and the results are shown by a size-frequencycurve in FIG. 6. As shown, the frequency of occurrence was the highestfor particles having sizes of ca. 6-7 μm but the polymer particlesobtained in Comparative Example 2 had a broader size distribution thanthose obtained in Examples 1 and 2.

As is clear from the foregoing description, the granulator used inimplementing the method of suspension polymerization of the presentinvention has a precise and uniform shear force generating field betweenthe rotating and stationary parts and fine droplets are produced by thestrong forces of shear that are generated in said field. Further, onlythe droplets that leave the shear force generating field for passingthrough a small clearance of a predetermined size are supplied into thepolymerization vessel. Since the droplets fed into the polymerizationvessel are free from coalescence, polymer particles having a narrow sizedistribution can be easily produced with size ranging distribution canbe easily produced with sizes ranging from ca. 30 μm down to as small as2-3μm.

Another embodiment of the present invention is described below ingreater detail with reference to FIGS. 7 to 11.

In this embodiment, substantially the same apparatus as that shown inFIG. 1 is used except for the disperser structure.

FIG. 7 is a schematic longitudinal section showing an example of thedisperser that can be sued in this embodiment. Shown by 111 is arotating turbine shaft having at its end the smooth-surfaced tubularrotating part 115. The shaft 111 is retained liquid-tight by means of anagitation seal 112. The stator 114 having an inner surface for definingan internal space is secured to the casing of the disperser. The tubularrotating part 115 is provided rotatably in the internal space of thestator. Shown by 113 is an outlet for dispersion, 116 is an inlet forthe continuous phase, 117 is an inlet for the disperse phase, and 118 isthe gap in which the dispersion is to be formed.

The method of this embodiment is implemented by the following procedure.A continuous phase component composed of a medium is retained in thevessel 1 whereas a disperse phase component composed of a monomericcomposition is retained in the vessel 2. The two components are suppliedsimultaneously and continuously through independent passageways into anarea close to the shear region in the disperser 5 by driving meteringpumps 4 provided in those passageways.

The continuous phase component introduced into the disperser 5 at inlet116 and the disperse phase component introduced at inlet 117 aresubjected to shear force as they pass through the gap 118 between thetubular rotating part 115 and the stator 114, whereby a dispersion isformed that consists of the disperse phase and the continuous phase. Thethus formed dispersion is discharged from the disperser at outlet 113and sent to the reaction vessel 3 via a passageway. Suspensionpolymerization is carried out in the reaction vessel 3 in the usualmanner.

The tubular rotating part in the disperser shown in FIG. 7 is taperedbut it may have other shapes.

The tubular rotating part preferably has a length of at least 10 mm. Thegap between the outer surface of the rotating part and the inner surfaceof the stationary part is preferably adjusted to lie within the range of0.01-5.0 mm, more preferably 0.05-2.0 mm. The tubular rotating part ispreferably rotated at a revolution speed of 3,000-50,000 rpm, morepreferably at 10,000-30,000 rpm.

In the present invention, the disperse phase component and thecontinuous phase component are supplied simultaneously into thedisperser at predetermined flow rates and, in the disperser, they aresubjected to shear force in the narrow gap between the tubular rotatingpart and the stationary part, whereby the efficiency of shearing actionis improved. Further, dispersing conditions such as the amount ofdroplets that pass through the shear region, their size and the ratio ofdisperse to continuous phase are placed under precise control to insurethat both the disperse and continuous phases are subjected to shearforce under conditions that are kept constant, whereby a dispersioncomprising droplets of a narrow size distribution are obtained.

If particles of the desired size cannot be obtained by a single passagethrough the shear region, another disperser may be provided so that thedispersion that passed through the first disperser is passed through thesecond disperser. In other words, the process described in the previousparagraphs may be repeated as many times as required.

Also in this embodiment, a suspension stabilizer is preferablyincorporated in the continuous phase.

As mentioned in connection with the first embodiment, suspensionstabilizers that are commonly used in suspension polymerization aresurface active materials having both a hydrophilic group and hydrophobicgroup in the molecule. Such surface active materials are those compoundsin which polar groups such as a hydroxyl group, a carboxyl group or asalt thereof, and a sulfone group or a salt thereof are present ashydrophilic groups and nonpolar groups such as aliphatic and aromaticgroups are present as hydrophobic groups and which are capable ofstabilizing the dispersed droplets by preventing their coalescence.

Examples of such suspension stabilizers include polyvinyl alcohol,casein, gelatin, cellulosic derivatives such as methyl cellulose,methylhydroxypropyl cellulose and ethyl cellulose, starch and itsderivatives, poly(meth)acrylic acid and salts thereof. Inorganic powdersuch as calcium phosphate powder and a fine silica powder are also oftenused as suspension stabilizers. These suspension stabilizers cover thesurfaces of droplets so that they will not coalesce or agglomerateduring polymerization.

If desired, neutral salts such as sodium chloride and sodium sulfate orsurfactants such as vinyl benzoate, sodium dodecylsulfonate and sodiumdodecylbenzenesulfonate may be added as aids for suspension stabilizers.

The disperse phase is formed of a disperse phase component composed of amonomeric composition. Any polymerizable monomers that are usable insuspension polymerization may be employed without particular limitationas the main component of the monomeric composition. Examples are:styrene and its derivatives such as styrene, o-methylstyrene,m-methylstyrene, p-methylstyrene, p-methyoxystyrene, p-phenylstyrene,p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene,2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene,p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene andp-n-decylstyrene; vinyl esters of organic acids such as vinyl acetate,vinyl propionate and vinyl benzoate; methacrylic acid and itsderivatives such as methacrylic acid, methyl methacrylate, ethylmethacrylate, propyl methacrylate, n-butyl methacrylate, n-octylmethacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearylmethacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate anddiethylaminoethyl methacrylate; acrylic acid and its derivatives such asacrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate,isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate,2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate andphenyl acrylate; vinyl ketones such as vinyl methyl ketone, vinyl hexylketone and vinyl isopropenyl ketone; N-vinyl compounds such asN-vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidone;vinyl-naphthalenes; and other polymerizable monomers such asacrylonitrile, methacrylonitrile and acrylamide. These monomers may beused on their own or they may be combined to various formulations.

Polymerization initiators are used in the present invention and they arepreferably soluble in polymerizable monomers. Exemplary polymerizationinitiators include azo or diazo compounds such as2,2'-azobisisotutyronitrile, 2,2'-azobis-(2,4-dimethyl-valeronitrile),and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and peroxidecompounds such as benzoyl peroxide, methyl ethyl ketone proxide andisopropyl peroxycarbonate.

In the present invention, two or more of the polymerization initiatorslisted above are preferably combined to various formulations for thepurpose of controlling the molecular weight and its distribution or forthe purpose of controlling the reaction time. If necessary, thepolymerization initiators may be used in combination with water-solubleinitiators such as ammonium persulfate and potassium persulfate.

The polymerization initiators are usually added in an amount of 0.1-20parts, preferably 1-5 parts, per 100 parts of the polymerizablemonomeric mixture.

Dyes, pigments and other ingredients may be added to the disperse phaseas required. If pigments such as carbon black is added to the dispersephase, it can be used in the manufacture of electrophotographic toners.

The disperse phase component and the continuous phase component that aredescribed above are introduced simultaneously into the disperser toprepare a dispersion comprising droplets having a predetermined size andsize distribution and the dispersion is then subjected to suspensionpolymerization. A reaction for suspension polymerization is usuallycarried out at polymerization temperatures of at least 50° C. whichshould be determined taking into account the temperature at which theadded polymerization initiator is dispersed. If the polymerizationtemperature is too high, the polymerization initiator will decomposerapidly to cause adverse effects on the molecular weight and othercharacteristics of the polymer.

The mechanism of action involved in the present invention is describedbelow.

In the present invention the disperse phase component and the continuousphase component are supplied via independent passageways directly intoan area close to the shear region in the disperse at desired flow rates.Since the disperser comprises a tubular rotating part having a smoothouter surface and a stationary part having a smooth inner surface, thenarrow gap between the two parts define the shear region in which thesupplied components are given shear force in an efficient way as theyare concentrated in that small shear region. Hence, according to thepresent invention, dispersing conditions such as the amount of dropletsthat pass through the shear region, their size and the ratio of disperseto continuous phase are placed under strict control to insure that boththe disperse and continuous phases are subjected to shear force underconditions that are kept constant, whereby a dispersion comprisingdroplets having a narrow size distribution is obtained.

EXAMPLES

The following examples are provided for the purpose of furtherillustrating the second embodiment but are in no way to be taken aslimiting.

Example 3

A solution as a continuous phase component was prepared by dissolvingpolyvinyl alcohol (product of Tokyo Kasei K.K.; degree ofpolymerization, ca. 2,000; degree of saponification, ca. 80%) and sodiumsulfate in water in respective amounts of 1% and 3% of water, the thusprepared continuous phase was charged into the container 21 shown inFIG. 1. A disperse phase component was prepared by dissolving 15 g of2,2'-azobisisobutyronitrile in a mixture of styrene (400 g) and butylacrylate (100 g) and charged into the container 22 shown in FIG. 1.

In the next step, the disperse phase component and the continuous phasecomponent were supplied into a disperser. The disperser had theconstruction shown in FIG. 7 and the rotating part having a diameter of50 mm at the thickest portion and that was spaced from the stationarypart by a gap of 1.00 mm was run at 9,000 rpm. The dispersion emergingfrom the disperser was directed into the reaction vessel, in which apolymerization reaction was carried out at 85° C. for 8 hours underagitation with a turbine impeller at 300 rpm.

The polymer composition thus obtained was cooled, filtered, washedthoroughly with water and centrifuged to produce a slurry of polymerparticles, which was then dried.

The size of the polymer particles was measured with a Coulter counter(aperture, 100 μm) and the results are shown by a size-frequency curvein FIG. 8. As shown, the polymer particles obtained in Example 1 had anarrow size distribution, with the frequency of occurrence being thehighest for particles having a size of ca. 5.1 μm.

Example 4

A solution as a continuous phase was prepared by dissolving calciumphosphate and sodium dodecylsulfonate in water in respective amounts of3% and 0.03% of water. The thus prepared continuous phase was chargedinto the container shown in FIG. 1. A disperse phase was prepared bydissolving 15 g of 2,2'-azobisisobutyronitrile in a mixture of styrene(400 g) and butyl acrylate (100 g) and charged into the container shownin FIG. 1. The subsequent procedures were the same as in Example 3.

The size of the polymer particles obtained was measured with a Coultercounter (aperture, 100 μm) and the results are shown by a size-frequencycurve in FIG. 9. As shown, the polymer particles obtained in Example 4had a narrow size distribution, with the frequency of occurrence beingthe highest for particles having a size of ca. 4.8 μm.

Having the features described, the method of suspension polymerizationof the present invention permits a disperse phase component and acontinuous phase component to be supplied via independent passagewaysdirectly into an area close to the shear region in a disperser atdesired flow rates. Further, shear force is exerted in a concentratedway in the narrow gap formed in the disperser between a tubular rotatingpart having a smooth outer surface and a stationary part having a smoothinner surface, and this enables the disperse phase to be dispersed inthe continuous phase in a very efficient manner without foaming. Hence,according to the present invention, particle size and its distributioncan be controlled in an easy way to permit the production of a polymeror a polymer composition that have a desired particle size and a narrowsize distribution. This feature renders the present inventionparticularly useful in the manufacture of polymer materials that arerequired to have very small sizes and narrow size distributions.

Further, according to the present invention, the disperse phasecomponent and the continuous phase component are prepared in independentvessels and supplied into the disperser through separate passageways, sothe ratio of the two phases can be changed without causing substantialeffects on other factors of manufacture. In addition, unlikeconventional techniques that use batch reactors, the method of thepresent invention can be performed efficiently irrespective of the sizeof reaction vessel. Because of these advantages, the present inventionincreases the "flexibility" of process for manufacturing polymers orpolymer compositions and is readily adaptable to scale up and otherdesign change in the process of manufacture.

It is apparent that the invention is not limited to the foregoingspecific examples and embodiments. For example, the asperities formed inthe confronted surfaces of the stator 12 and the rotor 13 in FIG. 2 maybe dispensed with and instead thereof, the smooth surfaces may beapplied as shown in FIG. 10. In the same way, the smooth surfaces of therotor 115 and the stator 118 shown in FIG. 7 may be displaced by theasperity or corrugation surfaces as shown in FIG. 11.

In using the asperities on the confronting surfaces of the stator andthe rotor, it is more preferable that the asperities or corrugations ofthe confronting surfaces be complementarily arranged to form a constantclearance while allowing the rotation of the rotor 115, as shown in FIG.12. With this arrangement, it is possible to increase an effectiveshearing surfaces since the complemental relation between the rotor andthe stator 114 is kept during the rotation of the rotor 115. Of course,it is apparent that the cross section of the corrugation is not limitedto the specific shape. It is possible to use asperities or corrugationshaving any cross sections such as triangular, rectangular, rounded ones.

What is claimed is:
 1. A method of suspension polymerization of amonomeric composition to produce uniformly sized particles having anarrow distribution, which method comprises the steps of:(a) retainingin independent vessels a disperse phase component including saidmonomeric composition and a continuous phase component; (b) supplyingsaid disperse phase component and said continuous phase component fromtheir respective vessels simultaneously and continuously throughassociated independent passageways into a uniform shear force generatingfield of a disperser, said disperser including a stationary part havingan inner surface and a tubular rotating part having an outer surface,said rotating part being rotatably provided within said stationary part,said inner surface and said outer surface having substantially the sameshape and defining a space therebetween having a substantially uniformthickness, said uniform shear force generating field being provided insaid space; (c) applying shear force to said disperse phase componentand said continuous phase component in said shear force generating fieldto form a dispersion having droplets of a desired size; (d) removingsaid dispersion from said shear force generating field; (e) introducingsaid dispersion into a polymerization vessel; and (f) completing apolymerization reaction to produce uniformly sized particles having anarrow distribution.
 2. The method according to claim 1, said inner androtatably provided within said stationary part and that has a outersurfaces being smooth.
 3. The method according to claim 1, said innerand outer surfaces having asperities.
 4. The method according to claim3, said stationary part having a rotary axis extending in a verticaldirection and said inner surface being confronted vertically with saidouter surface.
 5. The method according to claim 2, said stationary parthaving a rotary axis extending in a vertical direction and said innersurface being confronted vertically with said outer surface.
 6. Themethod according to claim 1, said tubular rotating part having a lengthof at least 10 mm.
 7. The method according to claim 1, wherein saidtubular rotating part rotates at a revolution speed of 3,000-50,000 rpm.8. The method according to claim 1, said uniform thickness being0.01-5.0 mm.
 9. The method according to claim 1, said dispersion fromstep (d) being dispersed at least one more time in at least one moredisperser before completing steps (e) and (f).
 10. The method accordingto claim 8, said uniform thickness being 0.05-2.0 mm.
 11. The methodaccording to claim 1, wherein said continuous phase component includes asuspension stabilizer.
 12. The method according to claim 1, wherein saiddisperse phase component includes 0.1-20 parts of a polymerizationinitiator per 100 parts of said monomeric composition.
 13. The methodaccording to claim 1, wherein said disperse phase component includes acompound selected from the group consisting of dyes and pigments. 14.The method according to claim 2, said inner and outer surfaces havingsubstantially the same shape.
 15. The method according to claim 7,wherein said revolution speed is 10,000-30,000 rpm.
 16. The methodaccording to claim 12, wherein said disperse phase component includes1-5 parts of said polymerization initiator per 100 parts of saidmonomeric composition.
 17. A method of suspension polymerization of amonomeric composition to produce uniformly sized particles having anarrow distribution, which method comprises the steps of:(a) retainingin independent vessels a disperse phase component including saidmonomeric composition and a continuous phase component; (b) supplyingsaid disperse phase component and said continuous phase component fromtheir respective vessels simultaneously and continuously throughassociated independent passageways into a uniform shear force generatingfield of a disperser, said disperser comprising a stationary part havinga first circular surface and a second annular surface surrounding andconcentric with said first surface, a rotating part having a thirdcircular surface confronting said first surface and a fourth annularsurface surrounding and concentric with said third surface andconfronting said second surface, said first surface and said thirdsurface having substantially the same shape and defining a spacetherebetween having a substantially uniform thickness, said uniformshear force generating field being disposed in said space, said secondsurface and said fourth surface having substantially the same shape anddefining a substantially uniform gap therebetween in a range of about1.8 mm or less; (c) applying shear force to said disperse phasecomponent and said continuous phase component in said shear forcegenerating field to form a dispersion having droplets of a desired size;(d) removing said dispersion from said shear force generating field,wherein substantially all of the dispersion passes through said gap; (e)introducing said dispersion into a polymerization vessel; and (f)completing a polymerization reaction to produce uniformly sizedparticles having a narrow distribution.
 18. The method according toclaim 17, wherein said first surface and said third surface aresubstantially smooth.
 19. The method according to claim 17, wherein atleast one of said first surface and said second surface have randomasperities having a height of 2 to 3 mm.
 20. The method according toclaim 17, wherein said stationary part has a rotary axis extending in avertical direction and said first surface is confronted horizontallywith said third surface.
 21. The method according to claim 17, whereinsaid rotating part rotates at revolution speed of 3,000-50,000 rpm.